JPH0766542B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnetic recording medium, and more particularly to a method of manufacturing a magnetic recording medium having an improved degree of orientation.

2. Description of the Related Art In recent years, high density recording has been required for magnetic recording media. However, in the internal magnetic recording method in which the direction of the magnetization, which has been widely used in the past, lies in the plane of the recording medium, the magnetizations repel each other, and it is impossible to achieve a high density above a certain level.

Therefore, a perpendicular magnetic recording system, which does not repel the magnetization because the direction of the magnetization is perpendicular to the surface of the recording medium, has been attracting attention.

Among them, in a magnetic recording medium using a coating type recording layer, generally, a magnetic coating is applied on a base film, and this is passed through a magnetic field in an undried state, and the easy axis of magnetization of the magnetic particles is set in the perpendicular direction. A manufacturing method is used in which the film is orientated and then dried.

In this case, as the orientation magnetic field, a method using an N-S facing magnet can be mentioned. In this method, the coating film is exposed to the orientation magnetic field for a short time, the orientation is disturbed by the influence of the demagnetizing field, and drying is performed. Since it takes a long time, there is a drawback that the orientation of the magnetic particles once oriented is disturbed again during that time.

In order to solve these drawbacks, a flat ferromagnetic particle is used as the magnetic particle, and a plurality of N-S facing magnets as shown in FIG. 3 are used.
A system in which 21,22 are arranged at intervals to form an orientation magnetic field, and a method of drying while passing through such a magnetic field and performing orientation (Japanese Patent Laid-Open Nos. 58-203631, 58-203632 and 58) No. 203633), and an N-S facing auxiliary magnet 33, 34 on the outlet side as shown in FIG.
A method has been proposed in which the N-S facing main magnets 31 and 32 having the magnets arranged at no intervals are used as an orientation magnetic field to orient the magnetic particles and then dry the particles (JP-A-59-139142). There is.

However, even these methods are still insufficient in terms of the degree of vertical orientation, surface roughness, etc., and further improvement is required.

II Object of the Invention An object of the present invention is to provide a method for producing a magnetic recording medium having an improved degree of vertical orientation and a good surface roughness.

III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below.

That is, according to the present invention, a magnetic coating material is applied onto a support, and this is an N-S opposing main magnet, and an auxiliary magnet array in which a plurality of magnetic poles of the same pole are arranged on the inlet side of both main magnets with a gap. The magnetic field strength of the magnetic poles forming the auxiliary magnet array is 10 to 70% of the magnetic field strength of the main magnet, and This is a method for manufacturing a magnetic recording medium, which comprises orienting the easy axis of magnetization of the particles substantially perpendicular to the film surface and drying.

IV Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.

The method for producing a magnetic recording medium of the present invention comprises applying a magnetic coating material on a support and passing it through a magnetic field as shown below,
The axis of easy magnetization of the magnetic particles in the coating film is oriented almost perpendicular to the film surface and the film is dried.

As the magnetic field, an N-S facing main magnet having an auxiliary magnet array in which a plurality of magnetic poles of the same pole are arranged with a gap is used on the inlet side of both main magnets of the N-S facing main magnet.

In this case, in order to improve the degree of orientation and surface roughness, the auxiliary magnet array is provided on the inlet side of the main magnet. And, it is sufficient that one or more sets of N-S facing main magnets having such an auxiliary magnet array are arranged.

FIG. 1 shows an embodiment in which an auxiliary magnet array is provided on the inlet side of the main magnet.

Next, description will be made with reference to FIG.

The magnets used in the present invention are NS facing main magnets 11 and 12, and both main magnets 11 and 12 are provided with auxiliary magnet rows 13 and 14 of the same pole on the inlet side of the coating material 1 in the traveling direction a. It is a thing.

The auxiliary magnet rows 13 and 14 are formed by arranging a plurality of magnetic poles 131 and 141 with gaps 132 and 142.

Although the number of such magnetic poles 131 and 141 is five in the illustrated example, it is preferable that the number is about 2 to 50. The gap is 0.5
It is good to set it to -10 mm, preferably 1-5 mm. And
The length of one magnetic pole is 0.5 to 10 mm, preferably about 1 to 5 mm.

Further, although FIG. 1 illustrates an example in which the auxiliary magnet rows 13 and 14 are integrated, the present invention is not limited to this mode.

Specific examples of such an auxiliary magnet array include (1) one in which the auxiliary magnet array is multi-polarized with a gap on the magnet surface, and (2) the auxiliary magnet array is a laminated body of an auxiliary magnet and a non-magnetic material. (3) Auxiliary magnet array in which a plurality of auxiliary magnets are embedded in a non-magnetic material, (4) Auxiliary magnet array in which a magnet material having a plurality of recesses is surface magnetized, (5) The auxiliary magnet array may be a permanent magnet such as a gap in the magnet row, but other electromagnets or solenoids may be provided.

It should be noted that the main magnet is not limited to one, and a plurality of main magnets may be used. At this time, at least one of the main magnets only needs to be provided with an auxiliary magnet array, and the main magnets may be arranged continuously without a gap, Various embodiments are possible.

In this case, it is preferable that the main magnet has a magnetic field strength of 1000 to 6000 G, preferably about 2000 to 6000 G, and the auxiliary magnet has one magnetic field strength of 100 to 5000 G, preferably 500 to 3000 G. The strength of the magnetic field of the magnet is 10 to 70%, more preferably 20 to 50%.

The main magnet may be a permanent magnet, an electromagnet, a solenoid, or the like, and the opposing magnetic pole gap is about 5 to 30 mm and the magnetic pole length is about 100 to 5000 mm.

With such a structure, the magnetic field oscillates, and the effect of this oscillating magnetic field improves the vertical orientation degree and the surface roughness.

The magnetic pole length of the auxiliary magnet array, the range of its gap, the magnetic field strength, and the like are the range of regions in which this oscillating magnetic field preferably acts.

FIG. 2 shows an embodiment in which a plurality of N-S facing main magnets having the above-mentioned auxiliary magnet array are used. Second
In the figure, the magnetization recording medium 1 running in the direction of arrow a is
First, it passes between the N-S opposing main magnets 15 and 16 of the first stage. The N-S facing main magnets 15, 16 are provided with auxiliary magnet rows 17, 18 of the same pole on the outlet side thereof. The second-stage N-S opposing main magnets 11 and 12 to be passed next are provided with auxiliary magnet rows 13 and 14 of the same pole on the inlet side.

Also in this case, the same effect as described above is realized, and the surface accuracy and the degree of orientation are further improved by using the main magnets having the auxiliary magnet rows in multiple stages.

And the auxiliary magnet array in the case of multiple stages as shown in FIG.
The magnetic pole lengths of 13, 14, 17, and 18, the range of the gap, the strength of the magnetic field, and the like are the same as above.

However, the main magnets 11 and 12 and the main magnets 15 and 16 of each stage, or the auxiliary magnet rows 13 and 14 and the auxiliary magnet rows 17 and 18 may not be the same.

In addition, when a plurality of N-S facing main magnets having the above-mentioned auxiliary magnet array are used, there is no particular limitation on the arrangement method, and the second
Various modifications other than those illustrated in the figure are possible.

That is, it is arbitrary whether the auxiliary magnet array of each stage is on the inlet side or the outlet side. However, in the final stage, it is preferable to provide the auxiliary magnet array on the inlet side.

To apply magnetic paint on the support, gravure coat,
Any coating method such as reverse roll coating, air knife coating, air doctor coating, blade coating, kiss coating or spray coating may be used.

The speed at which the above-mentioned coated material passes through the above-mentioned magnetic field is 2 to
About 500 m / min is preferable.

Drying after the orientation treatment is preferably performed at 30 to 150 ° C. and at a speed of about 2 to 500 m / min with a heater source such as hot air or a far infrared lamp.

The magnetic powder used in the magnetic coating material of the present invention is α-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-doped α-Fe ₂ O ₃ , Co-doped α-Fe ₂ O.
_3- Fe ₂ O ₃ solid solution, CrO ₂ , Co-based compound-adhered α-Fe ₂ O ₃ , Co-based compound-adhered Fe ₃ O ₄ , Ba ferrite, etc. granular, acicular, polyhedral, plate-shaped Etc., but Ba ferrite is particularly preferable. As the Ba ferrite, a hexagonal plate-shaped ferrite system is preferable, and further, in order to improve the degree of vertical orientation, it is preferable that the plate-shaped ratio (average grain size / average thickness) is 6 or more. The plate ratio can be controlled up to about 30.

As Ba ferrite, Ba ferrite such as BaFe ₁₂ O ₁₉ or B of this Ba ferrite is used.
Part of a, Fe is Ca, Sr, Pb, Co, Ni, Ti, Cr, Zn, In, M
Examples thereof include those substituted with n, Cu, Ge, Nb, Zr, and other metals.

The binder used in the magnetic paint may be various binders, but a binder obtained by curing a radiation curable compound is preferable.

Specific examples of the radiation-curable compound include acrylic double bonds such as acrylic acid, methacrylic acid, or ester compounds thereof having an unsaturated double bond having radical polymerizability, and an allyl double bond such as diallyl phthalate. It is a resin containing or introducing into a molecule of a thermoplastic resin a group such as a heavy bond, an unsaturated bond such as maleic acid or a maleic acid derivative, which is crosslinked or polymerized by irradiation with radiation. In addition, any compound having an unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used.

The resin containing or introduced into the molecule of the thermoplastic resin a group that is crosslinked or polymerized and dried by irradiation with radiation, is a resin containing maleic acid, fumaric acid, etc. From the viewpoint of radiation curability, etc., it is 1 to 40 mol%, preferably 10 to 30 mol% in the acid component.

As an example of the thermoplastic resin that can be modified into a radiation curable resin, the following vinyl chloride copolymers are particularly suitable.

Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acetic acid Vinyl-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, for example VRO manufactured by UCC
H, VYNC, VYEGX, VERR, VYES, VMCA, VAGH and the like.

Then, an acrylic double bond, a maleic acid double bond, and an allyl double bond are introduced into this to perform radiation-sensitive modification.

These may contain a carboxylic acid.

In addition, saturated polyester resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, fibrin derivatives and the like are preferable.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, An acrylic resin containing at least one of a hydroxyl group-containing acrylic ester and a methacrylic ester as a polymerization component is also effective.

And these are used individually or in combination of 2 or more types.

Elastomers or prepolymers can also be used, suitable examples being polyurethane elastomers or prepolymers.

The use of polyurethane is abrasion resistant and base film,
For example, it is particularly effective in that it has good adhesion to a PET film. As an example of the urethane compound, as the isocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene diisocyanate, 1,4
-Xylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-
Diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene diisocyanate, 4,4'-biphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, Desmodur L, Desmodur N, etc. Polyvalent isocyanate and linear saturated polyester (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,4-butanediol,
Polyhydric alcohols such as 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexanedimethanol and phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid Polycondensation with various saturated polybasic acids), linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol)
Polyurethane elastomers and prepolymers made of polycondensation products of various polyesters such as, caprolactam, hydroxyl-containing acrylic acid ester, and hydroxyl-containing methacrylic acid ester are effective.

By reacting a terminal isocyanate group or hydroxyl group of these urethane elastomers with a monomer having an acrylic double bond or an allyl double bond,
Radiation-sensitive modification is very effective. It also includes those containing OH, COOH or the like as a polar group at the terminal.

Further, a monomer having an unsaturated double bond having an active hydrogen that reacts with an isocyanate group and having a radiation-curable unsaturated double bond, such as a mono- or diglyceride of a long-chain fatty acid having an unsaturated double bond, is also included.

The combined use of these urethane elastomers with the above-mentioned acrylic modified base vinyl-based copolymer is particularly suitable for improving the degree of orientation and surface roughness.

In addition, acrylonitrile-butadiene copolymer elastomer and polybutadiene elastomer are also suitable.

Also cyclized polybutadiene, CBR-M90 made by Japan Synthetic Rubber
1 also has excellent properties when combined with a thermoplastic resin.

Other suitable thermoplastic elastomers and prepolymers thereof include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, isoprene rubber and cyclized products thereof (CIR701 manufactured by Japan Synthetic Rubber), epoxy-modified rubber, internal Elastomers such as plasticized saturated linear polyester (Toyobo Byron # 300) can also be effectively used by subjecting them to radiation-sensitive modification treatment.

In addition, oligomers and monomers having various radiation-curable unsaturated double bonds are also preferably used.

The weight ratio of binder to magnetic powder is about 1: 1 to 1: 9.

Further, the magnetic paint may contain a solvent, an inorganic pigment, a dispersant, a lubricant and the like.

As the support to be used, various resins such as polyester, polyamide and polyimide can be used.

Further, the support may be subjected to a base layer or a base treatment.

After forming the magnetic layer, various back coat layers and top coat layers can be formed.

V. Specific Actions and Effects of the Invention According to the present invention, an auxiliary magnet array in which a magnetic coating material is applied to a support and a plurality of magnetic poles of the same pole are arranged with gaps on the inlet sides of both N-S opposing main magnets The magnetic particles in the coating film are allowed to pass through between the N-S opposing main magnets and are oriented with the easy axis of magnetization almost perpendicular to the film surface, and are dried, so that the vertical orientation degree is improved and the surface roughness is also improved. A method of manufacturing a magnetic recording medium having excellent

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail by showing specific examples of the invention.

Example Using a hexagonal barium ferrite having an average particle size of 0.1 μm and a plate ratio of 8 (BaFe ₁₂ O ₁₉ partially substituted with Ba and Fe was synthesized by a hydrothermal synthesis method), magnetic properties were obtained as follows. Paint created.

Barium ferrite (Hc = 800) 120 parts by weight α-Al ₂ O ₃ (0.5 μ powder) 2 parts by weight Carbon black (20 mμ) 10 parts by weight Solvent (MEK / toluene: 50/50) 100 parts by weight The above composition The mixture was mixed in a ball mill for 3 hours to thoroughly wet the barium ferrite.

Next, as a binder, 6 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (containing maleic acid; MW40,000) (solid component conversion), acrylic double bond-introduced vinyl chloride-vinyl acetate-
Vinyl alcohol copolymer (containing maleic acid; MW20,00
0) 12 parts by weight (as calculated as solid content), acrylic double bond-introduced polyether urethane elastomer (MW40,000) 9 parts by weight (as calculated as solid content), pentaerythritol triacrylate 3 parts by weight, solvent MEK / toluene; 50 / 50) 200 parts by weight 4 parts by weight of stearic acid and 2 parts by weight of butyl stearate were mixed and dissolved.

This was placed in a ball mill containing the magnetic powder mixture, and mixed and dispersed again for 42 hours. Using the magnetic coating material thus obtained, gravure coating was performed on a 75 μm polyester film.

The sample thus prepared is referred to as sample A.

This sample A is used as an N-S opposing main magnet 11 and 12 having auxiliary magnets 131 and 141 rows of the same pole on the inlet side of both main magnets as shown in FIG. 1 (the magnetic field strength of the main magnet is 3000 G, the auxiliary magnet is A magnetic field strength of 1500 G) was passed at a speed of 30 m / min, and vertical alignment was performed while drying. Then, it dried with the far-infrared lamp. The main magnet is composed of 10 magnets each having a magnetic pole length of 50 mm arranged without a gap.

This is designated as Sample B.

In this case, the length of the magnetic poles of the auxiliary magnet array was 3 mm, the gap between the magnetic poles was 3 mm, and a stack of 20 auxiliary magnets was used between nonmagnetic materials (brass plates).

Next, the sample A is used as the N-S facing magnets 21 and 22 as shown in FIG.
(Magnetic field strength of 3000 G, magnetic pole length of 50 mm) 10 pieces were arranged at an interval of 10 cm, passed at a speed of 30 m / min, and vertically aligned while being dried.

Then, it was dried by a far infrared lamp.

This is designated as Sample C.

Further, Sample A was introduced between the N-S facing main magnets 31, 32 having the N-S facing auxiliary magnets 33, 34 attached on the outlet side as shown in FIG. Then, it dried similarly to the sample B.

This is designated as Sample D.

In this case, the main magnet has ten magnetic field strengths of 3000 G and a magnetic pole length of 50 mm arranged side by side. The magnetic field strength of one auxiliary magnet is 1500 G, and the magnetic pole length is 3 mm. Auxiliary magnet
Twenty were used.

The magnetic pole gap in Samples B, C and D was set to 15 mm.

The characteristics of samples B, C and D were investigated.

The characteristics were evaluated as follows.

(1) Vertical orientation degree The squareness ratio Br / Bm in the vertical direction of the magnetic tape was measured and the demagnetizing field was corrected.

(2) Surface Roughness R ₂₀ Taristep (manufactured by TAYLOR-HOBSON) was used to obtain a 20-point average method from a chart obtained.

The cutoff was 0.17 mm and the needle pressure was 0.1 × 2.5 μm.

The results are shown below.

Sample No. Degree of vertical orientation R ₂₀ B (invention) 0.80 0.05 μm C (comparison) 0.68 0.07 μm D (comparison) 0.68 0.07 μm From the above, the effect of the present invention is clear.

[Brief description of drawings]

FIG. 1 is a front view for explaining one embodiment of an N-S facing main magnet having auxiliary magnet rows of the same pole on the inlet side of both main magnets in the present invention. FIG. 2 is a front view for explaining one embodiment in which a plurality of N-S facing main magnets having auxiliary magnet rows according to the present invention are arranged. FIG. 3 is a front view for explaining an example of the conventional N-S facing magnets which are arranged at intervals. FIG. 4 is a front view for explaining an example of a conventional N-S facing main magnet with an N-S facing auxiliary magnet mounted on the exit side. Explanation of symbols 1 ... Coating material, 11,12,15,16 ... NS facing main magnet, 13,14,17,18 ... Auxiliary magnet array, 131,141,171,181 ... Magnetic pole, 132,142,172,182 ... Gap, 21, 22 ... NS facing magnet, 31,32 ... NS facing main magnet, 33,34 ... NS facing auxiliary magnet, a ... direction for passing coating material

Claims (5)

[Claims] 1. A magnetic paint is applied onto a support, and this is an N-S opposing main magnet, and an auxiliary magnet array in which a plurality of magnetic poles of the same pole are arranged with a gap on the inlet side of both main magnets. The magnetic particles in the coating film, which are arranged so as to face each other, are passed through between those in which the magnetic field strength of the magnetic poles forming the auxiliary magnet array is 10 to 70% of the magnetic field strength of the main magnet. A method of manufacturing a magnetic recording medium, characterized in that the axis of easy magnetization is oriented substantially perpendicular to the film surface and dried. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the gap is 0.5 to 10 mm. 3. The method for producing a magnetic recording medium according to claim 1, wherein the length of the magnetic poles of the auxiliary magnet array is 0.5 to 10 mm. 4. The method for manufacturing a magnetic recording medium according to claim 1, wherein a plurality of N-S facing main magnets each having an auxiliary magnet array are arranged. 5. The strength of the magnetic field of the NS facing main magnet is 1000 to 60.
The method of manufacturing a magnetic recording medium according to any one of claims 1 to 4, which is 00G.